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| United States Patent |
5,112,080
|
|
Okano
|
May 12, 1992
|
Sensor control circuit
Abstract
A sensor control circuit which includes a first sensor for detecting an
event; a second sensor having identical characteristics with those of the
first sensor for detecting the event at the same time; a processing unit
having a first processing section for receiving and processing a first
sensor signal from the first sensor and a second processing section for
receiving and processing a second sensor signal from the second sensor; a
first switching unit for switching in response to a first output from the
first processing section; a second switching unit for switching in
response to a second output from the second processing section; the first
and second processing sections being made so as to turn on the first
switching unit prior to the second switching unit in response to the first
and second sensor signals; and a monitor unit for preventing current
conduction to a load if the second switching unit is turned on prior to
the first switching unit.
| Inventors:
|
Okano; Masami (Saitama, JP)
|
| Assignee:
|
Zexel Corporation (Tokyo, JP)
|
| Appl. No.:
|
612913 |
| Filed:
|
November 14, 1990 |
Foreign Application Priority Data
| Current U.S. Class: |
280/735; 180/282; 307/10.1; 340/436 |
| Intern'l Class: |
B60R 021/32 |
| Field of Search: |
280/734,735
180/282
307/10.1
340/436
|
References Cited
U.S. Patent Documents
| 3889232 | Jun., 1975 | Bell | 280/735.
|
| 4166641 | Sep., 1979 | Okada et al. | 280/735.
|
| 4641041 | Feb., 1987 | Mattes et al. | 180/282.
|
| 4695075 | Sep., 1987 | Kamiji et al. | 280/735.
|
| 4851705 | Jul., 1989 | Musser et al. | 180/282.
|
| 4958851 | Sep., 1990 | Behr et al. | 180/282.
|
Primary Examiner: Rice; Kenneth R.
Attorney, Agent or Firm: Kanesaka & Takeuchi
Claims
I claim:
1. A sensor control circuit comprising:
a first sensor for detecting an event;
a second sensor having identical characteristics with those of said first
sensor for detecting said event at the same time;
a processing unit having a first processing section for receiving and
processing a first sensor signal from said first sensor and a second
processing section for receiving and processing a second sensor signal
from said second sensor;
first switching means for switching in response to a first output from said
first processing section;
second switching means for switching in response to a second output from
said second processing section;
said first and second processing sections being made so as to turn on said
first switching means prior to said second switching means in response to
said first and second sensor signals; and
monitor means for preventing current conduction to a load if said second
switching means is turned on prior to said first switching means.
2. The sensor control circuit of claim 1, which is connected to an actuator
of an airbag device.
3. The sensor control circuit of claim 2, wherein said first and second
processing sections integrate said first and second sensor signals from
said first and second sensors and determine by comparison whether
amplitudes of said sensor signals exceed a first threshold value and a
second threshold value, respectively, and output emergency signals for
turning on said first and second switching means when said amplitudes are
lower than said first and second threshold values, with said first
threshold value being set higher than said second threshold value.
4. A sensor control circuit connected to an actuator of an airbag device,
comprising:
a first sensor for detecting an event;
a second sensor having identical characteristics with those of said first
sensor for detecting said event at the same time;
a processing unit having a first processing section for receiving and
processing a first sensor signal from said first sensor and a second
processing section for receiving and processing a second sensor signal
from said second sensor;
first switching means for switching in response to a first output from said
first processing section;
second switching means for switching in response to a second output from
said second processing section;
said first and second processing sections being made so as to turn on said
first switching means prior to said second switching means in response to
said first and second sensor signals;
monitor means for preventing current conduction to a load if said second
switching means is turned on prior to said first switching means; and
said first switching means consisting of a pnp transistor having a base
connected to a first amplifier of the inverse type for receiving an output
from said first processing section; and an emitter connected to an energy
reservoir consisting of a capacitor of large capacitance;
said second switching means consisting of an npn transistor having a base
connected to a second aplifier for receiving an output from said second
processing section and an emitter grounded;
said actuator consisting of a heater connected across said collectors of
said first and second transistors so that when said first and second
transistors are turned on, said heater generates heat, which blows up an
explosive, causing a gas producing material to produce gases, which
instantly inflate an airbag.
5. The sensor control circuit of claim 4, wherein said monitor means
consisting of a comparator for comparing with a standard voltage V.sub.S a
controlled voltage V.sub.T applied to a positive terminal of said heater
which is not sufficiently high to cause said heater to generate heat and,
when V.sub.T <V.sub.S, outputs an inhibition signal for turning off said
first switching transistor, thereby preventing current conduction to said
heater.
6. A sensor control circuit comprising:
a first sensor for detecting an event;
a second sensor having identical characteristics with those of said first
sensor for detecting said event at the same time;
a processing unit having a first processing section for receiving and
processing a first sensor signal from said first sensor and a second
processing section for receiving and processing a second sensor signal
from said second sensor;
first switching means for switching in response to a first output from said
first processing section;
second switching means for switching in response to a second output from
said second processing section;
said first and second processing sections being made so as to turn on said
first switching means prior to said second switching means in response to
said first and second sensor signals;
a load connected in series with said first and second switching means;
monitor means for comparing a standard voltage V.sub.S with a control
voltage V.sub.T applied to a positive terminal of said load and, if said
second switching means is turned on prior to said first switching means
resulting in V.sub.T <V.sub.S, generates an inhibition signal for
preventing said first switching means from been turned on thereby
preventing current conduction to said load.
7. The sensor control circuit of claim 6, wherein said first switching
means comprises a pnp transistor having a base connected to a first
inversion type amplifier and an emitter connected to an energy reservoir
of a large capacity.
8. The sensor control circuit of claim 7, wherein said second switching
means comprises an npn transistor having a base connected to a second
amplifier for receiving an output of said second processing section and an
emitter grounded.
9. The sensor control circuit of claim 8, wherein said load comprises a
heater connected between collectors of said first and second transistors
and, when said first and second transistors are turned on, produces heat
which ignites an explosive causing a gas generating material to generate
gases thereby instantly inflating an airbag.
10. A sensor control circuit for a vehicle airbag control, comprising:
a first sensor for detecting an acceleration of a vehicle;
a second sensor having characteristics identical with those of said first
sensor and detecting said acceleration at the same time;
a processing unit including a first processing section for receiving and
processing a first sensor signal from said first sensor and a second
processing section for receiving and processing a second sensor signal
from said second sensor;
first switching means including a pnp transistor having a base connected to
a first amplifier of an inverse type for receiving an output from said
first processing section and an emitter connected to an energy reservor of
a large capacity to response to a first output from said first processing
section for performing a switching operation;
second switching means including an npn transistor having a base connected
to a second amplifier for receiving an output from said second processing
section and an emitter grounded to response to a second output from said
second processing section for performing a switching operation;
a heater connected in series between collectors of said first and second
switching means so that when both of said first and second transistors are
turn on, it generates heat for igniting an explosive to instantly inflate
an airbag;
monitor means for preventing current conduction to said load if said second
switching means is turned on prior to said first switching means.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to sensor control circuits suitable for
airbag devices.
2. Description of the Prior Art
While the number of passengers suffering injuries from automobile collision
increases with the increasing use of vehicles, airbag devices have been
put into practice which are mounted on the steering wheel or instrument
panel to instantly inflate the airbag upon collision to prevent the
passenger from crashing against the steering wheel or windshield glass.
The airbag devices are composed of an airbag, an actuator, and a sensor
control circuit.
The actuator is composed mainly of a heater which quickly converts electric
current into heat and an explosive which is blown up by the heat to ignite
a gas producing material. The produced gases instantly inflate the airbag.
The sensor control circuit is composed of a sensor for detecting the
acceleration of a vehicle, a processing unit for determining whether the
acceleration exceeds the threshold value because of a rapid deceleration
resulting from a collision or urgent braking, and a switching unit driven
by an emergency signal outputted from the processing unit when the
acceleration exceeds the threshold value to conduct current to the heater
of the actuator.
The processing unit is composed of a processing device such as a
microcomputer. In order to increase the reliability of airbag devices,
there are provided a pair of systems each consisting of the sensor and
processing section. In addition, a pair of switching sections are provided
across the heater so that only when both of the detecting systems detect
an abrupt stop, both of the switching sections are turned on to energize
the heater. In this way, the heater is prevented from being energized by a
malfunction of the detecting systems.
However, the processing unit composed of a microcomputer, for example, can
be runaway because of disturbance noise. When this happens, even if the
sensors do not detect any abrupt stop, both of the switching sections can
be turned on by the runaway processing unit to conduct current to the
heater. Consequently, the explosive is blown up to cause the gas producing
material to produce gases, which instantly inflate the airbag. As a
result, the airbag blocks the passenger's view, creating a very dangerous
driving condition. In addition, the blown airbag is wasted.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a sensor control
circuit with an anti-runaway measure.
According to the invention there is provided a sensor control circuit with
an anti-runaway measure, which includes a first sensor for detecting an
event; a second sensor having identical characteristics with those of the
first sensor for detecting the event at the same time; a processing unit
having a first processing section for receiving and processing a first
sensor signal from the first sensor and a second processing section for
receiving and processing a second sensor signal from the second sensor; a
first switching unit for switching in response to a first output from the
first processing section; a second switching unit for switching in
response to a second output from the second processing section; the first
and second processing sections being made so as to turn on the first
switching unit prior to the second switching unit in response to the first
and second sensor signals; and a monitor unit for preventing current
conduction to a load if the second switching unit is turned on prior to
the first switching unit.
The above and other objects, features, and advantages of the invention will
become more apparent from the following description when taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a sensor control circuit with anti-runaway
measure for use in an airbag device according to an embodiment of the
invention; and
FIG. 2 is a graph showing the relationship between the sensor signal and
the threshold value.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1, the sensor control circuit includes a pair of sensors 1 and 2
for detecting the acceleration of a vehicle; a processing unit 3, such as
microcomputer, having a pair of processing sections 30 and 31 for
processing the sensor signals S1 and S2 from the sensors 1 and 2; and a
pair of amplifiers 4 and 5 for amplifying the emergency signals E1 and E2
from the processing sections 30 and 31. It is noted that the amplifier 4
is of the inversion type.
The sensor control circuit also includes a pair of switching transistors 7
and 8, the collectors of which are connected across a heater 6 of the
actuator for controlling the current through the heater 6. The bases of
the pnp transistor 7 and the npn transistor 8 are connected to the outputs
of the amplifiers 4 and 5, respectively. Their emitters are connected to a
capacitor 9 of large capacitance as an energy reservoir and the ground,
respectively.
A comparator 10 of the sensor control circuit compares the voltage V.sub.T
at the positive terminal of the heater 6 with the standard voltage V.sub.S
and, when V.sub.T <V.sub.S, outputs an inhibition signal INH for
inhibiting the conduction of a current to the heater 6. A controlled power
source 11 outputs a voltage +5 V which is applied to the positive terminal
of the heater 6 via a series circuit of a resistor 12 and a diode 13. A
resistor 14 connected across the collector-emitter of the transistor 8
cooperate with resistor 12 to provide the controlled voltage V.sub.T which
is slightly lower than the voltage at which the heater 6 starts to
generate heat.
V.sub.T =(5-D.sub.F)(R2+R3)/(R1+R2+R3)
wherein
D.sub.F =the forward voltage drop of the diode 13,
R1= the resistance of the resistor 12,
R2= the resistance of the heater 6, and
R3= the resistance of the resistor 14.
The sensors 1 and 2 are designed so that it is possible to check their
detecting function by applying a test signal TS from the processing unit
3.
The sensor signals S1 and S2 from the sensors 1 and 2 vary with the time as
shown by curves A and C of FIG. 2. When there is a collision or urgent
braking at a time t1, for example, the vehicle speed drops rapidly so that
the amplitudes of the sensor signals S1 and S2 fall steeply.
The processing sections 30 and 31 receive the respective sensor signals S1
and S2 and perform an integration process for eliminating disturbance
noise, etc. Then, they perform a comparison process to determine whether
the amplitudes of the processed signals exceed the threshold values Th1
and Th2, respectively. That is, they determine whether the amplitudes of
the integrated signals S1 and S2 are lower than the threshold values Th1
and Th2, respectively. If S1<Th1 and S2<Th2, the processing sections 30
and 31 output emergency signals E1 and E2 to turn on the transistors 7 and
8, respectively. In order to prevent the processing sections 30 and 31
from inflating the airbag by mistake, the emergency signals E1 and E2 are
prioritized; that is, the threshold values Th1 and Th2 are set such that
Th1<Th2. Then, if there is an abrupt stop, the emergency signal E1 is
first outputted from the processing section 30 and, a little later, an
emergency signal E2 is outputted from the processing section 31 as shown
in FIG. 2. That is, the emergency signals E1 and E2 are prioritized in
output order by differentiating the threshold values Th1 and Th2.
The emergency signals E1 and E2 thus outputted are amplified by the
amplifiers 4 and 5 and applied to the bases of the transistors 7 and 8,
respectively, turning these transistors on. More specifically, the
transistor 7 is turned on first and, slightly later, the transistor 8 is
turned on. This permits the energy reservoir 9 to supply power to the
heater 6, which generates heat. The generated heat blows up the explosive
to permits a gas producing material to produce gases, which instantly
inflate the airbag.
Since the transistor 7 is turned on first, the controlled voltage V.sub.T
at the positive terminal of the heater 6 is never lower than the standard
voltage V.sub.S. Consequently, the output of the comparator 10 remains at
"H" level so that the inhibit signal INH is insignificant.
If the processing section 30 and/or 31 is out of order and outputs an
emergency signal E2 prior to E1, the transistor 8 is turned on first.
Consequently, the controlled voltage V.sub.T at the positive terminal of
the heater 6 is lower than the standard voltage V.sub.S before the
transistor 7 is turned on. It follows that the output signal INH of the
comparator 10 changes from "H" level to "L" level so that the inhibition
signal INH becomes significant.
When the inhibition signal INH is inputted to the amplifier 4, the base
potential of the transistor 7 is held at "H" level, preventing the
transistor 7 from being turned on. Consequently, the current to the heater
6 is interrupted before the heater 6 blows the explosive, thereby
preventing the airbag from being blown by mistake. In addition, the power
stored in the energy reservoir is saved. The inhibition signal INH at "L"
level is read into the processing unit 3 via a detection port P1 to record
the malfunction.
If the positive terminal of the heater 6 is grounded because of a
collision, the comparator 10 prevents discharge of the energy reservoir 9,
thereby eliminating the possibility that the engine control unit fails to
record the conditions of the collision because of total consumption of the
energy in the energy reservoir 9.
Although the controlled voltage V.sub.T at the positive terminal of the
heater 6 may be inputted to the processing unit 3 via an AD converter so
that the abnormal controlled voltage V.sub.T is detected through a
comparing process by software, it is preferred to use the comparator 10 as
described above because the AD conversion and comparing process can be
incomplete before the explosive is blown up or large amounts of energy are
lost between the AD conversion and the comparing process owing to a
failure to detect shortcircuit.
As has been described above, with the sensor control circuit according to
the invention, it is possible to not only prevent the airbag from being
inflated by the runaway processing section, thus preventing blocking the
driver's view but also save the airbag otherwise wasted.
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